1. Field of the Invention
The present invention relates to a method of manufacturing a low expansion material, and more specifically, to a method of manufacturing a material with low thermal expansion coefficient having excellent heat conductivity.
The present invention also relates to a semiconductor device using a substrate made of this low expansion material.
2. Description of the Related Art
The structure of a conventional semiconductor device is shown in FIG. 9. On a surface of a substrate 1 formed of Al, an insulating layer 2 and a wiring layer 3 are sequentially formed to obtain an Al circuit board A. A semiconductor element 5 is joined through solder 4 to the top face of the wiring layer 3.
Because the substrate 1 is formed of Al which has excellent heat conductivity, heat generated in the semiconductor element 5 is transmitted through the wiring layer 3 and the insulating layer 2 to the substrate 1 and is then efficiently radiated from the substrate 1 to the outside.
However, there is a large difference in thermal expansion coefficient between Si or other semiconductor material used in the semiconductor element 5 and Al forming the substrate 1. This difference is known to bring thermal stress between the Al circuit board A and the semiconductor element 5 upon temperature shift. When the thermal stress is large, the semiconductor element 5 could be warped and the solder 4 for joining the semiconductor element 5 may be cracked.
In an attempt to ease this thermal stress, semiconductor devices used in an environment with a wide temperature range, for example, automobiles, have a stress relieving member such as a heat spreader installed between the semiconductor element 5 and the Al circuit board A.
Installing such stress relieving member, however, raises a problem of increased heat resistance of the entire semiconductor device as well as complication by an increase in number of parts of the semiconductor device.
JP 2001-181066A proposes to ease thermal stress in a semiconductor device by using a substrate formed of a low thermal expansion composite material, which is obtained by impregnating a SiC porous body with Al or an Al alloy. This method, however, also has problems of complicated manufacture process and high manufacture cost because SiC particles have to be molded and sintered together with a binder to obtain the porous body and the obtained SiC porous body has to be impregnated with molten Al or Al alloy.